1. Field of the Invention
The present invention relates to a herbicidal composition for the control of annual bluegrass (Poa annua) comprising a microorganism belonging to the genus Xanthomonas.
2. Prior Art
Annual bluegrass which is growing abundantly at golf courses, city parks, athletic grounds and the like is the most strong, harmful weed in the turf. This weed is widely distributed throughout the world. In particular, annual bluegrass mixed in with the turf of golf courses, such as putting greens, tee grounds, fairways and roughs, comes into ears at all times in spite of frequent mowing, and scatters a large quantity of seeds into the turf all the year round. At present, there are a number of herbicides developed for control of annual bluegrass.
However, the effects of these chemical herbicides are very unstable at the site of use, and this has led to an increase in the amount of use and the frequency of application of these chemicals. The abundant use of agricultural chemicals at golf courses has particularly become a big social problem as one of the causes of environmental pollution. Among these chemical herbicides, there is no foliar treatment agent which can selectively kill annual bluegrass mixed in with Western turfgrasses, such as bentgrass, without harming the desired turfgrasses. Therefore, for the maintenance of bent green, manual weeding or even total renewal of turf is inevitably required, and the burden of costs therefor is tremendous.
On the other hand, microbial herbicides are being developed in the United States and Japan which comprise a bacterial pathogen to a plant, Xanthomonas campestris, and which selectively controls annual bluegrass without polluting the environment. Furthermore, a mixed application of Xanthomonas campestris and a chemical agent [a plant growth regulator, mefluidide (Embark.TM.)] for enhancing the herbicidal effect of the microbial herbicide has also been disclosed [Japanese Unexamined Patent Publication (Kohyo) No. 63-502438, U.S. Pat. No. 5,192,541].
However, the method of the prior art wherein the bacterial pathogen, Xanthomonas campestris, and the plant growth regulator are mixed and applied together has not solved at all a problem of herbicial spectrum which is the greatest advantage and, at the same time, a drawback of microbial herbicides, though this process can control annual bluegrass effectively. In other words, this prior art process can control only annual bluegrass.